Studies of the natural maintenance cycle of La Crosse (LAC) arbovirus endemic in deciduous forests of midwestern and eastern United States will be continued in field and laboratory for additional knowledge of viral, vector, vertebrate and environmental factors needed for eventual control of this arbovirus which each year causes California encephalitis in children. Fluorescent antibody and dissection techniques developed for visualization of LAC viral antigen in Aedes triseriatus will be applied to studies of salivary, transovarial, and venereal transmission in adults reared from larvae obtained from basal tree-holes in LAC endemic and non-endemic areas in western and southeastern Wisconsin. Isolation rates in Aedes triseriatus reared from pre-emergence season larval collections will be compared with those in adults obtained from these forested areas later in the season after they have had opportunity for horizontal transmission by venereal or viremic vertebrate means. Rates of antibodies in chipmunks and squirrels and isolates from Aedes triseriatus larvae and adults from these and previous studies in these areas will be compared to evaluate comparative roles in the maintenance cycle. Epidemiologic studies of cases of California encephalitis will be continued for evidence of circumstances of infection. BIBLIOGRAPHIC REFERENCE: Thompson, Wayne H. and Beaty, Barry J. Venereal Transmission of La Crosse (California Encephalitis) Arbovirus in Aedes triseriatus mosquitoes. Science, 1977 in press. Beaty, Barry J. and Thompson, Wayne H. The Delineation of La Crosse Arbovirus in Aedes triseriatus. The American Journal of Tropical Medicine and Hygiene, 25 (3):505-512, May, 1976.